Production of the fungal exopolysaccharide pullulan by batch-wise and continuous fermentation

A mutant strain of the deuteromycete Aureobasidium pullulans deficient in melanin synthesis was used to investigate the production of the exopolysaccharide pullulan and biomass, respectively. Shake-flask experiments with different carbon sources showed significant differences in pullulan elaboration. Sucrose was most suitable for pullulan synthesis among the carbon sources examined. Fermentations were carried out both batch-wise and continuously in a stirred vessel fermentator. In batch fermentations about 45% of the glucose offered was converted into pullulan at maximum formation rates of 0.16 g/l per hour using standard medium. The yield of polysaccharide could be maintained at 45% in continuous fermentations. At a dilution rate of 0.05 l/h, the formation rate of polysaccharide increased up to 0.35 g/l per hour. Alterations in the nitrogen content of the feed significantly affected the consumption rate of glucose and the production rate of polysaccharide, but final concentrations of biomass were hardly affected. Correspondence to: R. Schuster